My hypothesis, human civilization on Earth had peaks and falls and it is millions of years old. During one of the peaks that happened long millions of years ago, Mars was inhabitable and humans reached there, colonized it and made it another home. During the fall of that civilization, an apocalypse happened in Mars. The whole Mars branch of that era got annihilated by God as a wrath for their various sins. Later soon the Earth branch got devastated too. And a new dark age started where everything about civilization has been forgotten and humanity began repopulating the Earth and learning things again. That one also reached a peak and fell, too. And many other peaks and fall. By the ages passed, everything about colonization of Mars had been forgotten. Because no matter a new civilization rised, Mars was past recovery ever.